Glass fibers are produced by drawing multiple streams of molten glass at a given rate of speed through orifices or nozzles located in a heated container known in the fiber glass industry as a bushing. The bushings containing the molten glass are electrically heated and maintained at given temperatures to provide molten glass at the orifices or nozzles at a desired viscosity. The fibers drawn from the orifices or nozzles are gathered after they solidify into one or more strands and wound into one or more packages.
Bushings having 800 to 4,000 or more orifices or nozzles are commonplace in the industry, although bushings having fewer orifices or nozzles are also used. It is also common practice to produce more than one strand from a bushing. For example, two strands, four strands, or other numbers of strands are sometimes produced from a single bushing. Such an arrangement is generally referred to as a split-bushing. Typically, this is accomplished by dividing the bushing into sections or segments with each section or segment providing one strand. Splitting the bushing in this manner to produce more than one strand can require precise control of the bushing section temperatures so that the strands produced and wound into packages have the same yardage, i.e., the same yards per pound of glass or, viewed in another way, the same weight of glass strand per package collected for a given period of time.
The development of technology for adjusting bushing heat patterns and controlling formation of the individual strands, and in particular the coefficient of variation in the filament diameters, has progressed from moving manual fin coolers, which provide large but somewhat imprecise bushing adjustments, to three and four terminal controllers which adjust the electrical current in each section of the bushing by shunting a controlled current around sections of the bushing to produce variable heating. Bushing balance controllers that actively monitor and control the temperature of each bushing by shunting current have also been developed. Examples of bushing balance controllers are described in U.S. Pat. Nos. 5,051,121 and 5,071,459, which are hereby incorporated by reference. In the shunting of current around sections of the bushing using terminals, the terminals have been conventionally positioned on a single side of the bushing.